The reduction of vehicle gas emissions is a common goal in the design of modern motor vehicles. A popular device used to reduce vehicle emissions is the exhaust gas recirculation valve or EGR valve. EGR valves operate by returning a part of the engine's exhaust to the engine intake for reintroduction into the combustion cycle. By returning the exhaust to the engine's combustion cycle, the combustion temperature is lowered, thus reducing the formation of nitrogen oxides, compounds that are implicated in the formation of photochemical smog.
Although EGR valves are effective at reducing undesirable gas emissions, large solid particles, predominantly carbon particles, in the exhaust can cause the valve to stick open or closed. When the valve sticks open, it produces a vacuum leak in the engine, causing drivability problems with the engine, such as stalling at idle, and in severe cases can cause the car's power brakes to fail. When the valve sticks closed, combustion temperature is raised, increasing pollutants and sometimes causing spark knock and engine damage. As a result, the obstructed EGR must be removed for cleaning or replaced. Even worse, the EGR valve can be obstructed again and again, resulting in recurring maintenance problems.
There have been some attempts to prevent obstructing and clogging of the EGR valves with various types of filters. For example, U.S. Pat. No. 5,027,781 discloses a stainless steel filter affixed to a gasket to provide a barrier to large carbon particles in the exhaust gas. However, these filters eventually are obstructed and clogged with large carbon particles as well.